NumWorks + Raspberry Pi

A Raspberry Pi Zero 2 W running Linux inside a NumWorks calculator. The calculator's display shows the Pi desktop via SPI, and the keyboard sends input via UART.

Based on zardam's original project (2018), updated for modern Linux (Debian Trixie, Wayland, DRM/KMS).

What's in This Repo

Component	Location	Description
Firmware	firmware/	Git submodule: Upsilon fork with RPi app, SPI display bridge, UART keyboard, power control
DRM display driver	pi-linux/drm-spifb/	Kernel module: DRM/KMS tiny driver, XRGB8888 + RGB565, virtual resolution scaling
Device Tree overlay	pi-linux/overlay/	SPI device registration for the display driver
Keyboard daemon	pi-linux/uinput-serial-keyboard/	uinput daemon: UART key input + mouse mode, patched for Wayland
Pi config files	pi-linux/config/	Boot config, systemd service, keyboard layout
Power PCB	nwpi-pcb	Custom PCB: USB charging, LiPo battery, 5V boost for Pi
Documentation	docs/	Architecture, setup guides, firmware reference

How It Works

Calculator (STM32F412)              Pi Zero 2 W (BCM2710)
+----------------------+            +----------------------+
| RPi app              |            | labwc (Wayland)      |
|   keyboard scan loop |  UART TX   |   uinput daemon      |
|   64-bit key bitmap  |----------->|   /dev/ttyS0 115200  |
|                      |            |                      |
| SPI1 slave + DMA     |  SPI 62.5  |   drm-spifb          |
|   EXTI on CS (PA6)   |<-----------|   KMS -> SPI direct  |
|   -> LCD FSMC write  |   MHz      |   480x360 -> 320x240 |
+----------------------+            +----------------------+

The Pi renders its desktop at 480x360 (configurable). The DRM driver downscales to 320x240 RGB565 and pushes frames over SPI. The STM32 DMA writes pixels directly to the LCD. No intermediate copies.

The keyboard daemon reads UART hex-encoded key state, converts to Linux input events, and supports two modes: keyboard (letters/numbers) and mouse (arrow keys move cursor, OK = click).

Quick Start

1. Clone

git clone --recurse-submodules https://github.com/elektricM/numworks-pi.git
cd numworks-pi

2. Build & Flash Firmware (on your computer)

cd firmware
make MODEL=n0100 ENABLE_RPI=1 OMEGA_USERNAME="YourName" EPSILON_I18N=en -j$(nproc)
# Put calculator in DFU mode: hold reset + press 6
make MODEL=n0100 ENABLE_RPI=1 OMEGA_USERNAME="YourName" EPSILON_I18N=en epsilon_flash

3. Set Up the Pi

Flash Raspbian Trixie 32-bit Desktop to an SD card, enable SSH, boot, then:

# On the Pi — build display driver
cd pi-linux/drm-spifb
make
sudo make install
sudo depmod -a

# Install DT overlay
sudo ../scripts/install-overlay.sh

# Build keyboard daemon
cd ../uinput-serial-keyboard
gcc uinput.c -o uinput

# Install service
sudo cp ../config/nwinput.service /etc/systemd/system/
sudo systemctl daemon-reload
sudo systemctl enable nwinput

# Add to /boot/firmware/config.txt:
#   enable_uart=1
#   dtparam=spi=on
#   dtoverlay=numworks-spifb

# Remove console=serial0,115200 from /boot/firmware/cmdline.txt
# Set keyboard to US (both /etc/default/keyboard and ~/.config/labwc/environment)

sudo reboot

4. Wire & Test

See zardam's original blog post for wiring details and hardware requirements. Tap the RPi icon on the calculator to start.

What's Different from zardam's Original

	zardam (2018)	This project
Pi OS	Raspbian Stretch/Buster	Trixie (Debian 13)
Display stack	fbdev (spifb) + fbcp (dispmanx)	DRM/KMS (drm-spifb), direct
Compositor	X11	Wayland (labwc)
Display driver	spi_busnum_to_master()	Device Tree overlay
Resolution	Native 320x240 only	Virtual resolution (default 480x360)
Mouse input	X11 MouseKeys via NUMLOCK	Direct EV_REL events
Arrow keys	Numpad codes	Real arrow key codes
Firmware base	Epsilon	Upsilon (community fork)
UART	Worked by default	Fixed: consoleuart flavor + USART3 clock

Documentation

• Architecture — display pipeline, power design, keyboard protocol, driver internals
• Getting Started — full setup walkthrough
• Performance Investigation — FPS analysis, SPI optimization, NEON experiments
• Keyboard Map — full key mapping reference (modes, mouse, special characters)
• Running Doom — Chocolate Doom setup and controls
• Firmware Build Guide — build, flash, build flags
• Firmware Porting Notes — differences from zardam's epsilon
• UART Fix — consoleuart + USART3 clock fix
• Pi Setup (Trixie) — Wayland, DRM, keyboard layout
• Pi Setup Checklist — quick reference for fresh SD card
• Hardware & Wiring (zardam's blog) — original hardware guide

Credits

• Zardam — original design, firmware, SPI driver, keyboard daemon
• Upsilon / Omega / NumWorks — calculator firmware
• See CREDITS.md

License

Pi-side code and docs: GPL-2.0. Firmware submodule: CC BY-NC-SA 4.0 (see firmware/LICENSE.md).